A power tool can be adjusted by rotating and adjusting a control member to accommodate different situation during the operation of the power tool. For example, a torque adjusting sleeve of an electric drill can be rotated and adjusted to different output torques according to the operating load of the electric drill, a chuck of a hammer can be rotated and adjusted for adapting different bits, and a depth ruler of a router can be rotated and adjusted for suit different cutting depth, a planer is provided with a switch handle which is used for rotating and adjusting the distance between a front shoe and a rear shoe according to the cutting thickness of the planer. In fact, the operator hope to be reminded by some indicator when the adjustment member is rotating or adjusting during the operation, in case the operator performs incorrect operation and be not aware of the dangers. In general, the power tool works in the conditions accompanying with great vibration, the adjustment member of the power tool is easy to loose or reverse from its original position as the result of the vibration. It will be very easy to make dangers if the operator didn't get the caution in time. A power tool including a sound indicator for a adjustment member was disclosed in prior art, the frequency of the sound occurs at each revolution of the adjustment member is less than 25, the frequency of the sound is too lower to cause the operator to pay attention.
U.S. Pat. No. 6,805,206 discloses a hammer which includes a tool or a bit mounted on a spindle of the hammer, the hammer comprises a pair of ratchet wheels which enable impacting each other to cause sounds to remind of the operator when the tool or bit to be rotated to a determined orientation. As we know, the power tool is generally used for decorating or building and the environments full of noise, and the power tool itself also make a noise in use, the sound frequency of ratchet wheels of the hammer is about 20 (the times of a sound occurs at each revolution is about 20), the sound frequency is too lower to achieve the effect of remind.